Lithology, alteration, and mineralization in the Eastern Mexican Alkaline Province.

摘要

The Eastern Mexican Alkaline Province (EMAP) is a belt of Tertiary alkaline igneous intrusions extending from Coahuila to Veracruz. Lithologies range from felsic to mafic and from silica-saturated to undersaturated. Mineralization includes F ± Be associated with felsic lithologies, Mo ± Cu related to porphyries and pegmatites, Fe-oxide ± Cu skarn and Au associated with dioritic-monzonitic intrusions, REE ± Th related to carbonatites, and base metal ± Ag peripheral to igneous centers of diverse types. Two recurring features of the EMAP include (1) andradite-grossular garnet + magnetite skarn and endoskarn and (2) sodic-calcic alteration. These features resemble Fe-oxide(Cu-Au-REE) systems (e.g. Olympic Dam-type deposits), whose origins are controversial but increasingly associated with external saline fluids. The presence of Mesozoic evaporites in eastern Mexico supports the likelihood of evaporitic fluid involvement. However, observations that (1) mineralization styles are correlated with magma type and (2) certain alteration styles (e.g. K-silicate) are reminiscent of alteration by magmatic fluids, suggest that hydrothermal systems of eastern Mexico involve magmatic fluids as well.